1. Field of the Invention
This invention relates to power driven self propelled lawn mowers of the type that are steerable, and in particular of the type in which the rear wheels are steerable.
2. Discussion of the Prior Art
A problem in operating self propelled steerable lawn mowers, such as riding lawn tractors or walk behind mowers, is in maneuvering the mower when turning around a corner, a tree or other obstacle so as to cut the entire area of grass in a single pass, without having to back-up, do a second pass, or do excessive finish trimming. As a solution to the problem, lawn tractors have been made in which the rear wheel axles are pivoted so that the rear wheels can be steered, but this has still resulted in a relatively large turning radius, for example approximately 14" off the edge of the mower deck.
In another type of riding lawn mower, the rear wheel axles are not pivoted but are fixed, and a relatively complex friction drive transmission is used to transfer power independently to each rear wheel so that the two rear wheels can be turning at different speeds in the same direction, or can be turning in different directions to effect turning of the mower. In this type of mower, the front wheels are free pivoted casters which are not steerable. Also, this type of tractor is typically steered by operating a pair of levers.
Although the turning radius is essentially zero with the fixed axle type of friction drive mower, it requires a relatively complex transmission, since steering is totally dependent on regulating the speed and direction of each rear wheel independently. In addition, when cutting along the corner of a building, this type of vehicle can usually not be steered around the corner until after the rear wheels clear the edge of the corner so that an area of grass on the far side of the corner remains uncut, unless extreme caution is exercised to cover it in the first pass.